Difference Between Capstan and Turret Lathes

A capstan and turret lathe is a production lathe. It is used to manufacture any number of identical pieces in the minimum time.

In semi-automatic lathes, machining operations are done automatically. Functions other than machining, like loading and unloading of a job, the positioning of tools, and coolant operations, are done manually.

The turret head is mounted on the ram, fitted with turret slides that longitudinally slide on the saddle. The turret head has a hexagonal block having six faces with a bore for mounting six or more than six tools at a time.

The threaded hole on these faces is used to hold the tools. In the case of a Capstan Lathe, the hexagonal turret is mounted on a short slide or ram, which is again fitted with a saddle.

The saddle can be moved accordingly throughout the bed ways and can be fixed to the bed if necessary. It is specially used for bar-type jobs.

But in the case of Turret Lathe, the hexagonal turret is directly mounted on the saddle. The saddle can be moved through the bed ways. A turret lathe is generally used for chucking-type work.

What is a Capstan Lathe?

This machine carries the hexagonal turret on a ram or a short slide.

The ram slides longitudinally on a saddle positioned and clamped on the lathe bedways. This type of machine is lighter in construction and is suitable for machining bars in smaller diameters.

The tools are mounted on the square turret and the 6 faces of the hexagonal turret.

The feeding movement is obtained when the ram moves from the left to the right. And when the ram is moved backwards, the turret indexes automatically. And the tool mounted on the next face comes into operation.

What is a Turret Lathe?

A turret lathe is a form of metalworking lathe that is used for repetitive production of duplicate parts, which, by the nature of their cutting process, are usually interchangeable.

It evolved from earlier lathes with the addition of the turret, which is an indexable toolholder that allows multiple cutting operations to be performed, each with a different cutting tool, in easy, rapid succession, with no need for the operator to perform set-up tasks in between (such as installing or uninstalling tools) or to control the toolpath.

The latter is due to the toolpath’s being controlled by the machine, either in jig-like fashion, via the mechanical limits placed on it by the turret’s slide and stops, or via digitally-directed servomechanisms for computer numerical control lathes.

The name derives from the way early turrets took the general form of a flattened cylindrical block mounted to the lathe’s cross-slide, capable of rotating about the vertical axis and with toolholders projecting out to all sides, and thus vaguely resembled a swiveling gun turret.

Parts of Capstan And Turret Lathes

The turret lathe has essentially the same parts as the engine lathe except for the turret. And complex mechanisms are incorporated into it to make it suitable for mass production work.

#1. Bed.

The bed is a long box-like casting provided with accurate guideways upon which are mounted the carriage and turret saddle. The bed is designed to ensure strength, rigidity, and permanency of alignment under heavy-duty services.

#2. Headstock.

The headstock is made up of large casting. It is located at the left-hand end of the bed. The different types of headstocks in capstan and turret lathe are as follows:

Step Cone Pulley Driven Headstock

This is the simplest type of headstock and is fitted with small capstan lathes. Where the lathe is engaged in machining small and almost constant diameter of workpieces. Only three or four steps of the pulley can cater to the needs of the machine.

Electric Motor Driven Headstock

In an electric motor-driven headstock, both spindles of the machine, and the armature shaft of the motor are the same. Any speed difference or reversal is achieved by directly controlling the motor.

All Geared Headstock

On the larger lathes, the headstocks are geared and the different mechanism is employed for speed changing by actuating levers.

Preoperative or Preselective Headstock

It is an all-geared headstock with provisions for rapid stopping, starting, and speed charging for different operations and for pushing a button or pulling a lever.

For different operations and for turning different diameters, the speed of the spindle must change. The required speed for the next operation is selected beforehand. The speed-changing lever is placed at the selected position.

#3. Cross-Slide and Saddle.

In small capstan lathes, hand-operated cross slide is used which are clamped on the lathe bed at the required position. The larger lathes and heavy-duty turret lathes are equipped with usually two designs of the carriage.

Conventional Type of Carriage

The conventional type of carriage bridges the gap between the front and rear bed-ways. It is equipped with four station-type tool posts at the front and one rear tool post at the back of the cross slide.

Side-hung Type Carriage

The side-hung type carriage is generally fitted with heavy-duty turret lathes where the saddle rides on the top and bottom guideways on the front of the lathe bed.

This design facilitates the swinging of a larger diameter of the workpiece without being interfered with by the cross slide. The saddle and the cross slide may be fed longitudinally or crosswise by hand or power.

#4. Turret Saddle and Auxiliary Slide.

In a capstan lathe, the turret saddle bridges the gap between two bedways. The top face is accurately machined to provide a bearing surface for the auxiliary slide.

The saddle is adjusted on the lathe bedways and clamped at the desired position. The hexagonal turret is mounted on the auxiliary slide.

A turret is directly mounted on the top of the saddle, and any movement of the turret is affected by the movement of the saddle.

The movement of the turret may be affected by hand or power. The turret is a hexagonally shaped tool holder intended for holding six or more tools.

Working of the Capstan and Turret Lathe

All 6 faces of the turret can hold 6 or many different types of cutting tools. The turret can be automatically indexed, and each tool is brought in line with the lathe axis in a regular sequence. The workpieces are held in collets or chucks.

The longitudinal and crossfeed movement of the turret saddle and cross slide is controlled by adjustable stops.

These stops enable different tools set at different stations. To move by a fixed amount for performing different operations on repetitive workpieces without measuring the length or diameter of the machined surface in each case.

These special characteristics of a capstan and turret lathe enable it to perform a series of operations such as:

Turning.
Drilling.
Boring.
Thread cutting.
Reaming.
Necking.
Chamfering.
Cutting-off.
And many other operations in a regular sequence to produce a large number of identical pieces in less amount of time.